* window.h (struct window): Convert left_fringe_width

* window.h (struct window): Convert left_fringe_width
and right_fringe_width from Lisp_Objects to integers.
Adjust comment.
(WINDOW_FRINGE_COLS, WINDOW_LEFT_FRINGE_WIDTH)
(WINDOW_RIGHT_FRINGE_WIDTH): Adjust users.
* window.c (wset_left_fringe_width, wset_right_fringe_width):
Remove.
(make_window): Initialize new integer fields to -1.
(Fsplit_window_internal): Use direct assignment.
(Fset_window_configuration, save_window_save): Convert
Lisp_Object to integer and back where appropriate.
(Fset_window_fringes): Adjust user.  Return t if any fringe
was actually changed, and mention this in docstring.